Int. Adv. Otol. 2013; 9:(2) 263-267

CASE REPORT

Pyramidal Bony Bar Fixating the Lenticular Process: An Unusual Congenital Middle Anomaly

Vincent Van Rompaey, Bert De Foer, Thomas Somers, Jan Casselman, Erwin Offeciers

European Institute For Otorhinolaryngology – Head & Neck Surgery, Sint Augustinus Hospital, Antwerp (Wilrijk) (VVR, TS, EO) Department of Radiology, Sint Augustinus Hospital, Antwerp (Wilrijk) (BDF, JC)

We report the case of a male child with a bilateral pyramidal bony bar connecting and fixating the lenticular process of the to the bony posterior wall of the retrotympanum, thus obstructing ossicular chain movement and causing a bilateral conductive loss. Removal of the pyramidal bony bar was performed while sparing the stapedial muscle’s tendon. The ossicular chain regained its mobility and the membrane reflex could be elicited. The air-bone gap pure-tone average of 0.5, 1 and 2 kHz improved from 45 dB to 9.7 dB at 2 weeks and 6.7 dB at 4 months after surgery. The difference between the ossified stapedial muscle’s tendon, the elongated pyramidal eminence and our case will be discussed.

Submitted : 06 September 2012 Revised : 11 February 2012 Accepted : 07 January 2013

Introduction development. No problems had occurred during Congenital anomalies of the ossicular chain are rare and pregnancy, but the patient was admitted to the neonatal may present in various ways. Because they generally intensive care unit for one night due to mild respiratory occur behind an intact tympanic membrane, computed distress during the C-section. No abnormalities were tomography can be very useful in determining the type of detected by the paediatrician in the neonatal period. The deformity preoperatively. By means of a case report we universal new-born hearing screening was normal. The will demonstrate the subtle differences in ossicular chain patient did not experience recurrent upper respiratory anomalies and how this specific case of ossicular chain infections. There was no history of trauma. Family anomaly was treated surgically. history for hearing loss was negative. It was unclear to the parents at which age the hearing loss had occurred, Case Report nor could they confirm a rapid or progressive onset. He We report the case of a bilateral pyramidal bony bar had never experienced vertigo before. connecting and fixating the lenticular process of the During otoscopy a normal-appearing tympanic incus, obstructing ossicular chain movement and causing membrane was found bilaterally. Liminal audiometry a bilateral conductive hearing loss. revealed a bilateral conductive hearing loss with an air- A 5-year-old boy presented at the out-patient clinic with bone gap (ABG) of 45 dB on the right side and 38.3 dB hearing loss and delayed speech and language on the left side (pure-tone average of 0.5, 1 and 2 kHz).

Corresponding address: Erwin Offeciers, MD European Institute For Otorhinolaryngology – Head & Neck Surgery Sint Augustinus Hospital Oosterveldlaan 24, 2610 Antwerp (Wilrijk) Telephone: +32 3 443 36 04 Fax: +32 3 443 36 11 E-mail: [email protected]

Copyright 2005 © The Mediterranean Society of Otology and

263 The Journal of International Advanced Otology

Tympanometry demonstrated a type C curve on the right side (-90 daPa) and a type A tympanogram on the left side (-50 daPa). Several conditions were considered in the differential diagnosis including tympanosclerosis, otosclerosis, congenital ossicular chain fixation, absence of the oval or round window and a persistent stapedial artery. A temporal bone CT scan was performed and revealed a pyramidal bony bar connecting the lenticular process of the incus to the bony posterior wall of the retrotympanum (Figure 1). This abnormal structure seemed to be in continuity or in close proximity with the pyramidal eminence and the tendon of the stapedial muscle’s tendon. Additionally, the radiologists reported a high-riding bulb on the right side. No other causes of conductive hearing loss of middle or origin were found. A MRI scan was performed to evaluate the Figure 1. High-resolution CT images of the right temporal bone: a case of an elongated pyramidal eminence. Axial image. (1) posterior fossa and cerebellopontine angle, but this Lenticular process; (2) capitulum; (3) pyramidal bony bar examination did not reveal any abnormalities. or elongated pyramidal eminence. We decided to perform an exploratory tympanotomy on the right side (the worst hearing ear) to confirm the The ABG (pure-tone average of 0.5, 1 and 2 kHz) diagnosis suggested by imaging and to improve the improved from 45 dB preoperatively to 9.7 dB at 2 hearing if possible. A transmeatal approach was used to weeks and 6.7 dB at 4 months after surgery. explore the . Palpation of the ossicular chain Discussion revealed a mobile , but a fixation of the incus. To categorize this disorder according to Cremers’ The stapes superstructure was not visible. No round classification, we would suggest a class 3 congenital window membrane reflex could be elicited. Just lateral anomaly of the ossicular chain with a mobile stapes and in conjunction with the lateral face of the pyramidal footplate, caused by a pyramidal bony bar (without eminence, a bony bar originated at the bony wall of the ossification of the stapedial muscle’s tendon) and retrotympanum and connected with the lenticular consequent lenticular process fixation. [1] process of the incus, thus causing fixation. In our opinion, the pathology presented differs from the The pyramidal bony bar was removed using a microdrill elongated pyramidal eminence (which includes a and curette, while taking care to avoid injury to the prolonged circumferential ossification) and the ossified chorda tympani. The osseous prominence was fixed to stapedial muscle’s tendon (which affects the tendon itself), the lenticular process while leaving the stapes although it might share a common pathophysiological superstructure mobile and the long process of the incus. pathway with the former. Ossification of the tendon is The stapedial muscle’s tendon was intact and not probably caused by interhyale failing to differentiate into ossified. The stapes superstructure and footplate were fibrous tissue, while elongation of the pyramidal normal. The surgeon’s drawing and photographs taken eminence and the pyramidal bony bar are probably caused during surgery can be found in Figures 2 and 3. by prolonged condensation of mesenchymal tissue around Afterwards, the ossicular chain regained its mobility and the belly of the stapedial muscle. This hypothesis is based the round window reflex could be elicited by palpating upon the work of Rodriguez-Vazquez (personal the malleus handle. communication). [2]

264 Pyramidal Bony Bar Fixating the Lenticular Process: An Unusual Congenital Middle Ear Anomaly

Figure 2. Surgical drawing of the incus-stapes interface. (1) Pyramidal bony bar; (2) stapedial muscle’s tendon; (3) chorda tympani; (4) long process of the incus. A. The incus-stapes interface from the pyramidal eminence’s perspective. B. The incus-stapes interface from a different point of view to demonstrate the distinction between the stapedial muscle’s tendon and the pyramidal bony bar.

Figure 3. Intraoperative findings. Transmeatal view during exploratory tympanotomy. (1) Chorda tympani; (2) long process of the incus; (3) pyramidal bony bar; (4) round window niche (5) stapes superstructure (6) stapedial muscle’s tendon. A. Intraoperative view before removal of the pyramidal bony bar. B. Intraoperative view after removal of the pyramidal bony bar. The instrument (7) is pointed at the insertion of the stapedial muscle’s tendon in the stapes superstructure. Note that the tendon is intact.

265 The Journal of International Advanced Otology

Nandapalan and Tos have reported on isolated congenital stapes superstructure fixation including a pathology called stapes - pyramidal bony bar with normal stapedial muscle’s tendon , categorized as a class 2 congenital middle ear anomaly according to Cremers (i.e. a stapes ankylosis assoc iated with other congenital ossicular chain anomalies). [3] We think the case presented in our report has similarities to the stapes – pyramidal bony bar, but instead of fixating the stapes superstructure, it fixates the lenticular process (i.e. a lenticular process – pyramidal bony bar with normal stapedial muscle’s tendon ). Because it is the lenticular process which is fixated by the bony bar, we think it should be defined as a class 3 anomaly since the stapes footplate and superstructure per se are mobile.

Preoperative temporal bone CT scan can distinguish Figure 4. High-resolution CT images of the left temporal bone in between ossification of the stapedial muscle’s tendon another patient: a case of an ossified stapedial muscle’s tendon. Axial image. (1) Lenticular process; (2) stapes capitulum; (3) and osseous malformations of the pyramidal ossified stapedial muscle’s tendon. eminence. In case of an elongated pyramidal eminence, the triangular conus of the pyramidal eminence is touching the incudostapedial joint; in case of an ossified stapedial muscle’s tendon, the pyramidal Notwithstanding the dramatic improvement of the eminence is in the correct position while a linear resolution of CT scans, the final diagnosis is made my calcified structure (the ossified stapedial muscle’s middle ear inspection. Removal of the pyramidal bony tendon) can be observed (example in Figure 4). bar can restore ossicular chain mobility resulting in an However, preoperative CT scans do not allow excellent hearing outcome. differentiation between the elongated pyramidal Conflict of interest: None. eminence and the pyramidal bony bar (touching the stapes superstructure or lenticular process). References Until now, nineteen cases of stapedial muscle’s tendon 1. Teunissen EB, Cremers WR. Classification of ossification were reported in literature, seven cases congenital middle ear anomalies. Report on 144 . have been reported on elongation of the pyramidal Ann Otol Rhinol Laryngol 1993;102:606-12. eminence and six cases have been reported on a stapes 2. Rodriguez-Vazquez JF. Development of the - pyramidal bony bar without ossification of the and pyramidal eminence in humans. stapedial muscle’s tendon. [4-19] In our opinion, this is J Anat 2009;215:292-9. the first report of a pyramidal bony bar fixating the 3. Nandapalan V, Tos M. Isolated congenital stapes lenticular process (instead of the stapes ankylosis: an embryologic survey and literature superstructure). review. Am J Otol 2000;21:71-80. Conclusion 4. Thies C, Handrock M, Sperling K, Rcis A. Possible In this congenital malformation case a pyramidal bony autosomal recessive inheritance of progressive hearing bar is connecting the lenticular process of the incus to loss with stapes fixation. J Med Genet 1996;33:597-9. the bony posterior wall of the retrotympanum. By 5. Grant WE, Grant WJ. Stapedius tendon ossification: obstructing ossicular chain movement, it caused a a rare cause of congenital conductive hearing loss. J conductive hearing loss in early childhood. Laryngol Otol 1991;105:763-4.

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